Thanks for your reply Keith- those two operators are not running the event and the only UK based operator on the official Istanbul Marathon site has a very out of date website (2012)- the deal from RunfunTravel is about £280 per person for four nights accomodation and race entry- Excludes meals and flights.

The travel operator is mentioned on the official site- it just seems crazy cheap- which is why I am so sceptical of it! If this is a normal price for an abroad trip, I would appreciate confirmation from an experienced runner.